Concentrated nitrogen-containing fertilizers having increased alkaline earth metal uptake

ABSTRACT

Urea increases the solute content of a fertilizer comprising water and at least two different nitrate-containing compounds selected from the group consisting of ammonium nitrate, alkali metal nitrates, and alkaline earth metal nitrates. In addition, urea enhances plant uptake of alkaline earth metals. Particularly favored are quaternary aqueous solutions containing urea, calcium nitrate, and ammonium nitrate.

BACKGROUND

The present invention relates to (a) nitrogen-containing fertilizers,(b) methods for increasing alkaline earth metal uptake by plants, (c)methods for fertilizing plants, and (c) methods for manufacturingnitrogen-containing fertilizers.

Many plants need supplemental calcium for nutrition and diseaseprevention. However, plants have difficulty absorbing added calciumunless it is combined with one or more nitrogen compounds.

A material currently being used in agricultural practice is a ternaryaqueous solution comprising calcium nitrate and ammonium nitrate in abinary eutectic ratio. The ternary solution contains a mole ratio ofammonium nitrate to calcium nitrate of about 1.75. The maximum solutionconcentration that can be prepared from the ternary solution, whilemaintaining the crystallization temperature of the solution above or atabout -1.1° C. (about 30° F.), is about 30.9 weight percent ammoniumnitrate, about 36.2 weight percent calcium nitrate, and about 32.9weight percent water--for a total nitrogen content of about 17 weightpercent. (As used in the specification and claims, the term"crystallization temperature" means the temperature at which crystalsbegin to form in an aqueous solution as the temperature of the aqueoussolution is lowered; and the term "weight percent" means the weight of aparticular ingredient present in a solution divided by the total weightof all solubilized solutes and solvents present in the solution, thequotient being multiplied by 100%.)

SUMMARY OF THE INVENTION

In order to increase agronomic profitability, there is a need to furtherincrease the efficiency of plants to absorb calcium. In addition, thereis a need to increase the nitrogen concentration of nitrogen-containingfertilizers, thereby lowering costs by decreasing the amount offertilizer applied per unit area of land for any given nitrogenapplication rate.

The present invention satisfies both needs by providing aqueoussolutions comprising urea and at least two nitrate-containing compounds.(As used in the specification and claims, the term "nitrate-containingcompounds" means compounds selected from the group consisting ofammonium nitrate, alkali metal nitrates, alkaline earth metal nitrates,and mixtures thereof.) Preferably, the composition of the presentinvention is a quaternary aqueous solution comprising ammonium nitrate,calcium nitrate, and urea, with it being even more preferred that theammonium nitrate, calcium nitrate, and urea be present in a ternaryeutectic ratio. The quaternary solution can be formulated to contain ahigher total nitrogen content, while maintaining the crystallizationtemperature of the solution at or below about -1.1° C. (about 30° F.).For example, the most preferred quaternary solution of the presentinvention has a crystallization temperature of about -1.1° C. (about 30°F.) and contains about 25.5 weight percent ammonium nitrate, about 30weight percent calcium nitrate, about 17.2 weight percent urea, andabout 27.3 weight percent water. Accordingly, the total nitrogen contentof this preferred quaternary solution is about 22 weight percent-- anincrease of about 30 percent over the prior art ternary solution.Because the quaternary solution has a higher nitrogen concentration thanthe ternary solution, a smaller amount of the quaternary solution isrequired to be applied per unit area for a given nitrogen applicationrate. In addition, as demonstrated hereinafter in Example 2,substantially more calcium is absorbed by a plant from theurea-containing solution of the present invention than from a solutiondevoid of urea.

BRIEF DESCRIPTION OF DRAWING

The increased calcium uptake by plants and the increased nitrogencontent of aqueous fertilizer solutions, as well as other features,aspects, and advantages of the invention will become better understoodwith reference to the following description, appended claims, andaccompanying drawing wherein the sole Figure is a graphical plot ofcrystallization temperature versus urea concentration. The data plottedin the Figure were obtained from an experiment (described in Example 1,hereinafter) which entailed adding incremental amounts of urea to aternary aqueous solution containing ammonium nitrate and calcium nitratein an eutectic ratio and observing the crystallization temperature ofthe resulting quaternary solutions.

DETAILED DESCRIPTION OF THE INVENTION

The fertilizer of the present invention is an aqueous solutioncomprising urea and at least two nitrate-containing compounds.Preferably, the nitrate-containing compounds are selected from the groupconsisting of ammonium nitrate, sodium nitrate, potassium nitrate,magnesium nitrate, and calcium nitrate, with ammonium nitrate andcalcium nitrate being preferred. The total concentration of thenitrate-containing compounds in the composition of the present inventionare generally less than about 75 weight percent. More commonly, thetotal concentration of the nitrate-containing compounds in thecomposition of the present invention is about 40 to about 70, e.g.,about 45 to about 65, and preferably about 50 to about 60, weightpercent.

In a quaternary aqueous solution comprising ammonium nitrate, calciumnitrate, and urea, the mole ratio of ammonium nitrate to calcium nitrateis generally about 1 to about 3, often about 1.25 to about 2.5, and moreoften about 1.5 to about 2. Preferably, the mole ratio of ammoniumnitrate to calcium nitrate is about 1.75±0.2, more preferably about1.75±0.15, and even more preferably about 1.75±0.1. In addition, themole ratio of urea to calcium nitrate is generally about 0.1 to about 5,often about 0.5 to about 4, more often about 1 to about 3, and mostoften about 1.2 to about 2.2. Preferably, the mole ratio of urea tocalcium nitrate is about 1.7±0.4, more preferably about 1.7±0.3, andeven more preferably about 1.7±0.2. The most preferred ammoniumnitrate-, calcium nitrate-, and urea-containing quaternary aqueoussolution has a mole ratio of ammonium nitrate to calcium nitrate ofabout 1.75±0.05 and a mole ratio of urea to calcium nitrate of about1.7±0.1.

The aqueous solutions of the present invention generally have acrystallization temperature of less than about 12.8° C. (55° F.), oftenless than about 12.2° C. (54° F.), more often less than about 11.7° C.(53° F.), even more often less than about 11.1° C. (52° F.), and mostoften less than about 10.6° C. (51° F.). In addition, the aqueoussolutions commonly have a crystallization temperature greater than about-12.2° C. (10° F.), often greater than about -11.7° C. (11° F.), moreoften greater than about -11.1° C. (12° F.), and even more often greaterthan about -10.6° C. (13° F.).

For temperate climates, the aqueous solutions of the present inventionusually have a crystallization temperature of about -10° C. to about-1.1° C. (14° F. to 30° F.). For example, the crystallizationtemperature of the aqueous solutions manufactured for use in temperateclimates can be about -3.9° C. (25° F.) or about -5° C. (23° F.) orabout -6.7° C. (20° F.) or about -9.4° C. (15° F.) or any othertemperature within the approximate range of -10° C. to -1.1° C. (14° F.to 30° F.).

When formulated for use in tropical areas (e.g., Hawaii), the solutionsof the present invention preferably have a crystallization temperaturewithin the range of about -1.1° C. to about 10° C. (30° F. to 50° F.).The crystallization temperature of the solutions manufactured for use intropical climates can be any temperature within the approximate -1.1° C.to 10° C. (30° F. to 50° F.) temperature range (e.g., 0° C. (32° F.) orabout 1.7° C. (35° F.) or about 4.4° C. (40° F.) or about 5° C. (41° F.)or about 7.2° C. (45° F.)).

The compositions of the present invention generally contain at leastabout 5, often at least about 10, and more often at least about 15,weight percent total dissolved nitrogen. (As used in the specificationand claims, the term "total dissolved nitrogen" means the concentrationof nitrogen in the solution resulting from the solubilization of ureaand the nitrate-containing compounds in the solution. When the term"total dissolved nitrogen" is employed in a more limited sense to meanthe concentration of nitrogen in the solution resulting from thesolubilization of urea, ammonium nitrate, and calcium nitrate, the termis qualified by the phrase "from urea, ammonium nitrate, and calciumnitrate.") The urea-, ammonium nitrate-, and calcium nitrate-containingquaternary aqueous solutions intended for use in temperate climatestypically comprise at least about 16, more typically at least about 17,even more typically at least about 18, and most typically at least about19, weight percent total dissolved nitrogen. Preferably, the urea-,ammonium nitrate-, and calcium nitrate-containing quaternary aqueoussolutions manufactured for temperate climate usage comprise at leastabout 20, more preferably at least about 21, and most preferably about22, weight percent total dissolved nitrogen. When manufactured for usein tropical areas, the urea-, ammonium nitrate-, and calciumnitrate-containing quaternary aqueous solutions preferably comprise atleast about 22, more preferably at least about 23, even more preferablyat least about 24, and most preferably about 25, weight percent totaldissolved nitrogen.

The solutions of the present invention are also describable in terms ofthe concentrations of their various constituents. The following Table Isets forth approximate weight percents for quaternary solutionscontaining urea, ammonium nitrate, calcium nitrate, and water.

                  TABLE I                                                         ______________________________________                                        Constituent Concentrations, Weight Percent                                             Ammonium    Calcium                                                  Urea     Nitrate     Nitrate     Water                                        ______________________________________                                          0.1 - ˜25                                                                        ˜20 - ˜35                                                                     ˜25 - ˜40                                                                   ≦ ˜33                           ˜10 - ˜25                                                                  ˜25 ± 5                                                                          ˜30 ± 5                                                                          ˜27 ± 5                             ˜13 - ˜24                                                                  ˜25 ± 4                                                                          ˜30 ± 4                                                                          ˜27 ± 4                             ˜15 - ˜22                                                                  ˜25 ± 3                                                                          ˜30 ± 3                                                                          ˜27 ± 3                             ˜16 - ˜21                                                                  ˜25 ± 2                                                                          ˜30 ± 2                                                                          ˜27 ± 2                             ˜17 - ˜20                                                                  ˜25 ± 1                                                                          ˜30 ± 1                                                                          ˜27 ± 1                             ______________________________________                                    

Urea is present in the solutions of the present invention generally in aconcentration of about 0.5 to about 25, often about 1 to about 24, moreoften about 2 to about 23, even more often about 3 to about 22, and mostoften about 4 to about 21, weight percent. Typically, the solutions ofthe present invention contain at least about 5, preferably at leastabout 6, more preferably at least about 7, even more preferably at leastabout 8, and most preferably at least about 9, weight percent urea.

The urea-, ammonium nitrate-, and calcium nitrate-containing aqueoussolutions of the present invention commonly contain at least about 10,often at least about 11, more often at least about 12, even more oftenat least about 13, and most often at least about 14 weight percent urea.When such solutions are manufactured for use in temperate climates, theypreferably contain at least about 15, more preferably at least about 16,and most preferably about 17, weight percent urea. When made for usagein tropical areas, the urea-, ammonium nitrate, and calciumnitrate-containing aqueous solutions preferably comprise at least about18, more preferably at least about 19, and most preferably about 20,weight percent urea.

An interesting aspect of the present invention is that thecrystallization temperature of some, if not all, of the urea-, ammoniumnitrate-, and calcium nitrate-containing aqueous solutions is less thanthe crystallization temperature of a comparative composition whichcompositionally differs from the solution solely in that the comparativecomposition is devoid of urea. (The mole ratios of the ingredientscommon to both the comparative composition and the solution are thesame.) This phenomenon is unexpected because the crystallizationtemperature of an aqueous solution generally increases as an additionalsolute is added to the solution. Hence, the maximum solute concentrationin a quaternary aqueous solution is usually less than the maximum soluteconcentration in a ternary aqueous solution composed of two of thesolutes present in the quaternary solution. Accordingly, the presentinvention provides for the preparation of quaternary aqueous solutionshaving a higher nitrogen content than previously obtainable with ternaryaqueous solutions containing ammonium nitrate and calcium nitrate in thesame mole ratio--a very surprising result.

Optionally, one or more additives may be present in the solutions ofthis invention. Exemplary additives are other macronutrient-containingcompounds and other micronutrient-containing compounds. (As used in thespecification and claims, the term "macronutrient" means an elementselected from the group consisting of oxygen, carbon, hydrogen,nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium; and theterm "micronutrient" means an element selected from the group consistingof iron, manganese, boron, zinc, copper, molybdenum, and chlorine.)Macronutrient-containing compounds and micronutrient-containingcompounds are well known to those skilled in the art and need not beelaborated upon in detail. Suffice to say that all themacronutrient-containing compounds present in the composition of thepresent invention constitute generally less than about 25, and sometimesless than about 15 or about 10 or even about 5, weight percent, whileall the micronutrient-containing compounds in the composition accountfor typically less than about 10, and often less than about 5 or about 1or even about 0.5, weight percent.

While other macronutrient-containing compounds andmicronutrient-containing compounds are optionally present, thecomposition of the present invention frequently contains less than about5, more often less than about 3, and quite commonly less than about 1,weight percent of a compound or ingredient other than thenitrate-containing compounds, urea, and water. In fact, the preferredquaternary solution of the present invention often contains justammonium nitrate, calcium nitrate, urea, and water, with traceimpurities generally, but not necessarily, being present.

One method for preparing the solution of the present invention entailsfirst mixing the nitrate-containing compounds and water. To thissolution is then added urea. A surprising phenomenon occurs during thepreparation of the urea-, ammonium nitrate-, and calciumnitrate-containing aqueous solutions, namely, urea readily dissolves inan ammonium nitrate- and calcium nitrate-containing aqueous solution atan ambient temperature. (As used in the specification and claims, theterm "ambient temperature" means a temperature of about 0° C. (32° F.)to about 40° C. (104° F.).) The ambient temperature at which the urea isdissolved in the ammonium nitrate- and calcium nitrate-containingaqueous solution is generally less than about 35° C. (95° F.) and quiteoften less than about 30° C. (86° F.). In addition, urea is dissolved inthe ammonium nitrate- and calcium nitrate-containing aqueous solution atan ambient temperature frequently greater than about 5° C. (41° F.),more commonly greater than about 10° C. (50° F.), and very frequentlygreater than about 15° C. (59° F.). Most frequently, the dissolution ofurea in the ammonium nitrate- and calcium nitrate-containing aqueoussolution takes place at a temperature of about 20° C. (68° F.) to about25° C. (77° F.).

The easy dissolution of urea in an ammonia nitrate- and calciumnitrate-containing aqueous solution is unexpected because thedissolution of urea in water is highly endothermic--requiring the inputof heat, in addition to that present in the ambient environment, todissolve urea in water. In contrast to dissolving urea in only water,when urea is dissolved in an ammonium nitrate- and calciumnitrate-containing aqueous solution to form the preferred composition ofthe present invention, only a slight endotherm results. Hence,sufficient heat exists in the ambient environment for preparing theurea-, ammonium nitrate-, and calcium nitrate-containing aqueoussolutions of the invention.

When employed, the optional additives are preferably added to the urea-and nitrate-containing aqueous solution.

The compositions of the present invention are applied to the soil,applied directly to plants, and/or introduced into irrigation waterusing techniques well known to those skilled in the art for handlingliquid fertilizers. The aqueous compositions are suitable forapplication on any agricultural or horticulture crop, and areparticularly desirable for use on vegetables (e.g., lettuce and celery)and potatoes as well as other vegetation susceptible to calciumdeficiency-induced diseases. The application rate depends on theparticular crop being treated, with most application rates fallingwithin the range of about 5.6 to about 560 kilograms (kg) per hectare (5to 500 pounds per acre) total nitrogen.

EXAMPLES

The following examples are intended to illustrate and not limit theinvention. Example 1 demonstrates the decrease in crystallizationtemperature and the increase in solubility achievable by adding urea toan aqueous solution of ammonium nitrate and calcium nitrate. Theincrease in calcium uptake in the presence of urea is shown in Example2.

EXAMPLE 1 Crystallization Temperature Depression, Increased Solubility

Incremental amounts of urea were added to a solution which initiallycomprised about 30.9 weight percent ammonium nitrate, about 36.2 weightpercent calcium nitrate, and about 32.9 weight percent water. The moleratio of ammonium nitrate to calcium nitrate in all the solutionsemployed in Example 1 was about 1.75. The temperature of each of theresulting solutions was lowered and the respective crystallizationtemperatures were noted and recorded. The results are set forth in thefollowing Table A and plotted in the sole Figure.

                                      TABLE A                                     __________________________________________________________________________    Results Of Comparative Tests Demonstrating                                    Crystallization Temperature Depression And Increased Solubility                      Concentration, Weight Percent                                          Comparative                                                                          Ammonium                                                                            Calcium     Total                                                                              CO(NH.sub.2).sub.2 :                                                                Crystallization                           Test   Nitrate                                                                             Nitrate                                                                            Urea                                                                             Water                                                                             Nitrogen                                                                           Ca(NO.sub.3).sub.2.sup.a                                                            Temperature, °C.                   __________________________________________________________________________                                        (°F.)                              1 (control)                                                                          30.9  36.2  0 32.9                                                                              17   0     -1.1  (30)                                2      29.4  34.4  5 31.3                                                                              18.5 0.40:1                                                                              -5.6  (22)                                3      27.8  32.6 10 29.6                                                                              19.9 0.84:1                                                                              -7.2  (19)                                4      27.2  31.9 12 29  20.5 1.03:1                                                                              -7.8  (18)                                5      26.6  31.1 14 28.3                                                                              21.1 1.23:1                                                                              -9.4  (15)                                6      26    30.4 16 27.6                                                                              21.6 1.44:1                                                                              -10   (14)                                7      25.3  29.7 18 27  22.2 1.66:1                                                                              2.8   (37)                                8      24.7  29   20 26.3                                                                              22.8 1.88:1                                                                              10.6  (51)                                __________________________________________________________________________     .sup.a Mole ratio of urea to calcium nitrate.                            

As set forth in Table A and graphically indicated in the Figure, whenincreasing amounts of urea are added to an ammonium nitrate- and calciumnitrate-containing aqueous solution initially devoid of urea, thecrystallization temperature of the solution decreases until a minimum ofabout -10° C. (14° F.) is reached at an urea concentration of about 16weight percent. The data listed in Table A and plotted in the Figurealso indicate that the solute concentration in the solution increases(and, therefore, the water content of the solution decreases) as theurea concentration of the solution reaches about 17 weight percent(while maintaining the crystallization temperature of the solution at orbelow about -1.1° C. (30° F.)).

EXAMPLE 2 Increased Plant Uptake of Calcium

In another set of comparative experiments, leaves of growing mature SJ-1cotton plants were dipped in about a 2 weight percent nitrogen solutioncontaining the same calcium concentration (about 900 mg/l Ca). One ofthe nitrogen solutions (solution (a)) was a ternary aqueous solutioncontaining a eutectic mole ratio of ammonium nitrate to calcium nitrateof about 1.75 and composed of about 30.9 weight percent ammoniumnitrate, about 36.2 weight percent calcium nitrate, and about 32.9weight percent water. The other nitrogen solution (solution (b)) was aquaternary aqueous solution comprising about 25.5 weight percentammonium nitrate, about 30 weight percent calcium nitrate, about 17.2weight percent urea, and about 27.3 weight percent water and having amole ratio of about 1.75 moles of ammonium nitrate per mole of calciumnitrate and a mole ratio of about 2 moles of urea per mole of calciumnitrate. Each leaf was about 7 cm×10 cm.

For a control, four randomly selected leaves were dipped in the abovesolution (a) and another four randomly selected leaves were dipped inthe above solution (b). After about 20 minutes, each of these eightleaves was rinsed with the same quantity of distilled water.

Another four randomly selected leaves were dipped in solution (a) and anadditional four randomly selected leaves were dipped in solution (b).These latter eight leaves were then rinsed with distilled water about 24hours after dipping. (The same quantity of distilled water was employedin both the 20 minute and the 24 hour experiments.)

The unassimilated calcium was determined by measuring the calciumcontent of the rinsate. The results of these measurements were recordedand are listed in the following Table B.

                  TABLE B                                                         ______________________________________                                        Plant Calcium Uptake                                                          Control, mg Ca/l, 20 min.                                                                       Treatment, mg Ca/l, 24 hrs.                                 Solution (a)                                                                            Solution (b)                                                                              Solution (a)                                                                             Solution (b)                                 ______________________________________                                               11.2            9.6         6.2        4.3                                    9.5             11.3        7          4.6                                    12.1            9.8         5.9        5                                      11              12.5        6.8        3.9                             Ave.:  11     Ave.:    10.8 Ave.:  6.5 Ave.:  4.4                             ______________________________________                                    

Based upon the data set forth in Table B, the average calcium absorbedfrom solution (a) by the cotton leaf was about 41 percent, whereas theaverage calcium absorbed from an exemplary composition of the presentinvention, namely, solution (b), was about 59 percent. Accordingly,about 18 percent more calcium was absorbed from the urea-, ammoniumnitrate-, and calcium nitrate-containing aqueous solution (b) than fromsolution (a), i.e., an ammonium nitrate- and calcium nitrate-containingaqueous solution devoid of urea.

Thus, the urea-, ammonium nitrate-, and calcium nitrate-containingaqueous solutions of the present invention provide for the production ofa new nitrogen-calcium fertilizer having (a) an increased solids content(and, therefore, a reduced shipping, storage, and application costbecause the fertilizer has a higher active ingredient content) and (b)an increased calcium nutrition efficiency (due to the enhancement ofplant calcium uptake).

Although the present invention has been described in detail withreference to some preferred versions, other versions are possible. Forexample, in addition to calcium, urea can be employed in conjunctionwith other alkaline earth metals (e.g., magnesium) to increased plantuptake of such elements. Also, solutions designed to increase the uptakeof alkaline earth metals need only contain urea, water, and an alkalineearth metal. (For example, a calcium nitrate- and urea-containingaqueous solution can be made by combining about 60.96 g Ca(NO₃)₂.4H₂ O,about 11.29 g urea, and about 27.74 g water to produce a clear liquidwith a crystallization temperature of about 3.9° C. (39° F.).)Furthermore, while it is desirable from a cost perspective to simplydissolve urea in a nitrate-containing solution to form the compositionof the present invention, heat can be used to expedite the dissolutionof urea in the nitrate-containing solution. Therefore, the spirit andscope of the appended claims should not necessarily be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. An aqueous solution comprising:(a) about 1 toabout 25 weight percent urea, (b) about 20 to about 35 weight percentammonium nitrate, (c) about 25 to about 40 weight percent calciumnitrate, and (d) about 22 to about 33 weight percent water; and having:(A) a mole ratio of ammonium nitrate to calcium nitrate of 1.5 to about3, (B) a mole ratio of urea to calcium nitrate of about 0.1 to about 5,(C) a total dissolved nitrogen content from ammonium nitrate, calciumnitrate, and urea of at least 18 weight percent, and (D) acrystallization temperature of about -1.1° C. (30° F.) or less.
 2. Theaqueous solution of claim 1 comprising about 10 to about 25 weightpercent urea, about 20 to about 30 weight percent ammonium nitrate,about 25 to about 35 weight percent calcium nitrate, and less than about32 weight percent water.
 3. The aqueous solution of claim 1 comprisingabout 13 to about 24 weight percent urea, about 21 to about 29 weightpercent ammonium nitrate, about 26 to about 34 weight percent calciumnitrate, and less than about 31 weight percent water.
 4. The aqueoussolution of claim 1 comprising about 15 to about 22 weight percent urea,about 22 to about 28 weight percent ammonium nitrate, about 27 to about33 weight percent calcium nitrate, and less than about 30 weight percentwater.
 5. The aqueous solution of claim 1 comprising about 16 to about21 weight percent urea, about 23 to about 27 weight percent ammoniumnitrate, about 28 to about 32 weight percent calcium nitrate, and lessthan about 29 weight percent water.
 6. The aqueous solution of claim 1comprising about 17 to about 20 weight percent urea, about 24 to about26 weight percent ammonium nitrate, about 29 to about 31 weight percentcalcium nitrate, and less than about 28 weight percent water.
 7. Thesolution of claim 1 having a mole ratio of ammonium nitrate to calciumnitrate of 1.5 to about 2.5 and a mole ratio of urea to calcium nitrateof about 0.5 to about 4 moles.
 8. The solution of claim 1 having a moleratio of ammonium nitrate to calcium nitrate of 1.5 to about 2 and amole ratio of urea to calcium nitrate of about 1 to about 3 moles. 9.The solution of claim 1 having a mole ratio of ammonium nitrate tocalcium nitrate of about 1.55 to about 1.95 and a mole ratio of urea tocalcium nitrate of about 1.2 to about 2.2 moles.
 10. The solution ofclaim 1 having a mole ratio of ammonium nitrate to calcium nitrate ofabout 1.6 to about 1.9 and a mole ratio of urea to calcium nitrate ofabout 1.3 to about 2.1 moles.
 11. The solution of claim 1 having a moleratio of ammonium nitrate to calcium nitrate of about 1.65 to about 1.85and a mole ratio of urea to calcium nitrate of about 1.4 to about 2moles.
 12. The solution of claim 1 having a mole ratio of ammoniumnitrate to calcium nitrate of about 1.7 to about 1.8 and a mole ratio ofurea to calcium nitrate of about 1.5 to about 1.9 moles.
 13. Thesolution of claim 1 having a total dissolved nitrogen content fromammonium nitrate, calcium nitrate, and urea of at least 19 weightpercent.
 14. The solution of claim 1 having a total dissolved nitrogencontent from ammonium nitrate, calcium nitrate, and urea of at least 20weight percent.
 15. The solution of claim 1 having a total dissolvednitrogen content from ammonium nitrate, calcium nitrate, and urea of atleast 21 weight percent.
 16. The solution of claim 1 having a totaldissolved nitrogen content from ammonium nitrate, calcium nitrate, andurea of at least 22 weight percent.
 17. The aqueous solution of claim 1comprising about 5 to about 25 weight percent urea, about 20 to about 35weight percent ammonium nitrate, about 25 to about 40 weight percentcalcium nitrate, and about 22 to about 33 weight percent water.
 18. Theaqueous solution of claim 1 comprising about 10 to about 25 weightpercent urea, about 20 to about 35 weight percent ammonium nitrate,about 25 to about 40 weight percent calcium nitrate, and about 22 toabout 33 weight percent water.
 19. The solution of claim 1 having atotal potassium-containing compound concentration of less than about 25weight percent.
 20. The solution of claim 1 having a totalpotassium-containing compound concentration of less than about 15 weightpercent.
 21. The solution of claim 1 having a total potassium-containingcompound concentration of less than about 10 weight percent.
 22. Thesolution of claim 1 having a total potassium-containing compoundconcentration of less than about 5 weight percent.
 23. The solution ofclaim 1 having a total potassium-containing compound concentration ofless than about 1 weight percent.
 24. The solution of claim 1 comprisingabout 10 to about 25 weight percent urea.
 25. The solution of claim 1comprising about 12 to about 25 weight percent urea.
 26. The solution ofclaim 1 comprising about 14 to about 25 weight percent urea.
 27. Thesolution of claim 1 comprising about 16 to about 25 weight percent urea.28. The solution of claim 1 comprising about 18 to about 25 weightpercent urea.
 29. The solution of claim 1 comprising about 20 to about25 weight percent urea.
 30. The solution of claim 1 wherein the totalconcentration of ammonium nitrate and the nitrogen-containing compoundsin the solution is about 50 to about 75 weight percent.
 31. The solutionof claim 30 comprising about 12 to about 25 weight percent urea.
 32. Thesolution of claim 30 comprising about 14 to about 25 weight percenturea.
 33. The solution of claim 30 comprising about 16 to about 25weight percent urea.
 34. The solution of claim 30 comprising about 18 toabout 25 weight percent urea.
 35. The solution of claim 30 comprisingabout 20 to about 25 weight percent urea.
 36. The solution of claim 1having a mole ratio of ammonium nitrate to calcium nitrate of 1.5 toabout 2.5.
 37. The solution of claim 1 having a mole ratio of ammoniumnitrate to calcium nitrate of 1.5 to about
 2. 38. The solution of claim1 having a mole ratio of ammonium nitrate to calcium nitrate of about1.55 to about 1.95.
 39. The solution of claim 1 having a mole ratio ofammonium nitrate to calcium nitrate of about 1.6 to about 1.9.
 40. Thesolution of claim 1 having a mole ratio of ammonium nitrate to calciumnitrate of about 1.65 to about 1.85.
 41. The solution of claim 1 havinga mole ratio of ammonium nitrate to calcium nitrate of about 1.7 toabout 1.8.
 42. The solution of claim 1 having a mole ratio of urea tocalcium nitrate of about 0.5 to about 4 moles.
 43. The solution of claim1 having a mole ratio of urea to calcium nitrate of about 1 to about 3moles.
 44. The solution of claim 1 having a mole ratio of urea tocalcium nitrate of about 1.2 to about 2.2 moles.
 45. The solution ofclaim 1 having a mole ratio of urea to calcium nitrate of about 1.3 toabout 2.1 moles.
 46. The solution of claim 1 having a mole ratio of ureato calcium nitrate of about 1.4 to about 2 moles.
 47. The solution ofclaim 1 having a mole ratio of urea to calcium nitrate of about 1.5 toabout 1.9 moles.
 48. The solution of claim 1 having a mole ratio of ureato calcium nitrate of about 1.6 to about 1.8 moles.
 49. The aqueoussolution of claim 1 comprising about 20 to about 30 weight percentammonium nitrate.
 50. The aqueous solution of claim 1 comprising about21 to about 29 weight percent ammonium nitrate.
 51. The aqueous solutionof claim 1 comprising about 22 to about 28 weight percent ammoniumnitrate.
 52. The aqueous solution of claim 1 comprising about 23 toabout 27 weight percent ammonium nitrate.
 53. The aqueous solution ofclaim 1 comprising about 24 to about 26 weight percent ammonium nitrate.54. The aqueous solution of claim 1 comprising about 25 to about 35weight percent calcium nitrate.
 55. The aqueous solution of claim 1comprising about 26 to about 34 weight percent calcium nitrate.
 56. Theaqueous solution of claim 1 comprising about 27 to about 33 weightpercent calcium nitrate.
 57. The aqueous solution of claim 1 comprisingabout 28 to about 32 weight percent calcium nitrate.
 58. The aqueoussolution of claim 1 comprising about 29 to about 31 weight percentcalcium nitrate.
 59. The aqueous solution of claim 1 consistingessentially of urea, ammonium nitrate, calcium nitrate, and water. 60.The aqueous solution of claim 1 consisting of urea, ammonium nitrate,calcium nitrate, and water.